The focus of the proposed research is on DMT1 (Divalent Metal Transporter 1) and its role in Mn ingestion and inhalation. We have chosen the Belgrade rat for these studies since its DMT1 gene contains glycine-to-arginine substitution at amino acid codon 185 (G185R). This defective allele encodes a protein with little or no activity in iron uptake assays and transfection studies suggest that the mutant protein is rapidly degraded. Functionally, DMT1 mediates the uptake of many different divalent metal cations including Fe+2 and Mn+2. Not only does the Belgrade rat suffer from profoundly impaired Fe metabolism, these animals also display significant defects in Mn metabolism. Dietary Fe absorption is modulated by iron status, and DMT1 expression is up-regulated by Fe deficiency. Dietary Fe overload diminishes Mn accumulation in the brain while Fe deficiency is conversely associated with increased Mn in the central nervous system. These lines of evidence further suggest that Mn absorption is modulated by Fe status due to the regulation of DMT1 expression. However, while the role for this transporter in dietary Fe absorption has been established, and its function in intestinal Mn absorption is predicted, whether DMT1 is also involved in metal absorption in the lung remains unknown. Thus, it is possible that the absorption of inhaled Fe and Mn is also affected by iron status via DMT1 regulation. The major underlying hypothesis of this grant proposal is that Fe and Mn utilize the same carrier transport system in the respiratory and gastrointestinal tracts such that absorption of both metals is up-regulated upon iron-deficiency. If so, neurological complications of poor Fe status could be compound by an increased vulnerability to the toxic effects of Mn exposure. If these hypotheses are correct, children suffering from Fe deficiency may be particularly at risk for Mn neurotoxicity because of the relationship between carrier systems for these two metals. The Belgrade rat provides the model system to address test our hypothesis.